Removing Heavy Metals in a Ballasted Process

ABSTRACT

A system for treating metal-contaminated wastewater includes a primary treatment sub-system, a secondary treatment sub-system, and a tertiary treatment sub-system. The tertiary treatment sub-system includes a reactor tank, a source of ballast material, a source of coagulant, a solids-liquid separator, and a controller configured to recycle ballasted solids from the solids-liquid separator to the reactor tank an amount sufficient to generate metal hydroxide floc in the reactor tank to reduce a concentration of dissolved metal in the reactor tank.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Application Ser. No. 62/346,017 titled “REMOVING HEAVYMETALS IN A BALLASTED PROCESS,” filed on Jun. 6, 2016, which is hereinincorporated by reference in its entirety.

FIELD OF TECHNOLOGY

One or more aspects of the disclosure relate generally to water andwastewater treatment, and more particularly to systems and methods forremoving dissolved metal contaminants from wastewater in a tertiarytreatment system.

SUMMARY

In accordance with an aspect of the present disclosure, there isprovided a system for treating wastewater. The system comprises aprimary treatment sub-system and a secondary treatment sub-system influid communication downstream of the primary treatment sub-system. Thesecondary treatment sub-system is configured to remove biologicalcontaminants from the wastewater and produce a partially treatedwastewater including a dissolved metal. The system further includes atertiary treatment sub-system in fluid communication downstream of thesecondary treatment sub-system. The tertiary treatment sub-systemcomprises a reactor tank configured and arranged to receive thepartially treated wastewater from the secondary treatment sub-system,the reactor tank including at least one inlet and an outlet, a source ofa ballast material fluidly connected to the reactor tank, a source ofcoagulant fluidly connected to the reactor tank, a solids-liquidseparator having an inlet fluidly connected to the outlet of the reactortank and including a solids-lean effluent outlet and a ballasted solidsoutlet, the solids-liquid separator configured to separate ballastedeffluent from the outlet of the reactor tank into a solids-lean effluentand ballasted solids, to discharge the solids-lean effluent from thesolids-lean effluent outlet, and to discharge the ballasted solids fromthe ballasted solids outlet, a recycle conduit having an inlet fluidlyconnected to the ballasted solids outlet, and an outlet fluidlyconnected to the reactor tank, and a controller configured to recycle aportion of the ballasted solids from the ballasted solids outlet of thesolids-liquid separator to the reactor tank through the recycle conduitin an amount sufficient to generate an amount of metal hydroxide floc inthe reactor tank sufficient to reduce a concentration of dissolved metalin the reactor tank.

In some embodiments, the controller is configured to recycle the portionof the ballasted solids from the ballasted solids outlet of thesolids-liquid separator to the reactor tank through the recycle conduitin an amount sufficient to generate an amount of metal hydroxide floc inthe reactor tank sufficient to reduce a concentration of dissolved metalin the reactor tank to below about 10 micrograms/literor to below about5 micrograms/liter.

In some embodiments, the controller is configured to recycle betweenabout 5% and about 25% of ballasted solids separated from the ballastedeffluent in the solids-liquid separator to the reactor tank. Thecontroller may be configured to recycle about 10% of ballasted solidsseparated from the ballasted effluent in the solids-liquid separator tothe reactor tank.

In some embodiments, the system further comprises a source of a metalprecipitant in fluid communication with the reactor tank. The metalprecipitant may be a sulfide-containing compound.

In some embodiments, the system further comprises a source of a pHadjustment agent in fluid communication with the reactor tank. Thecontroller may be further configured to control a quantity of pHadjustment agent introduced into the reactor tank to achieve a pH in thereactor tank at which a compound including the dissolved metal issubstantially insoluble.

In some embodiments, the system further comprises a source of aflocculant in fluid communication with the reactor tank and/or a sourceof an adsorbant in fluid communication with the reactor tank and/or asource of a pH adjustment agent in fluid communication with the reactortank.

In some embodiments, the system further comprises a ballast recoverysystem in fluid communication with the ballasted solids outlet of thesolids-liquid separator, the ballast recovery system configured toseparate ballast from the ballasted solids and return the separatedballast to one of the reactor tank and the source of ballast material.

In some embodiments, the secondary treatment system comprises a secondreactor tank configured and arranged to remove biological contaminantsfrom the wastewater, and a ballast recycle system configured to return aportion of ballasted solids output from the second reactor tank to thesecond reactor tank.

In accordance with another aspect, there is provided a method fortreating wastewater. The method comprises treating the wastewater inprimary treatment sub-system and a secondary treatment sub-system toproduce a partially treated wastewater having a reduced concentration oforganic contaminants as compared to the wastewater and including adissolved metal, introducing the partially treated wastewater into areactor tank with a ballast material and a coagulant to form ballastedsolids, introducing a ballasted effluent from the reactor tank includingthe ballasted solids into a solids-liquid separator, separating theballasted effluent into ballasted solids and a solids-lean effluent inthe solids-liquid separator, and recycling a portion of the ballastedsolids from the solids-liquid separator to the reactor tank in an amountsufficient to generate an amount of metal hydroxide floc in the reactortank sufficient to reduce a concentration of dissolved metal in thereactor tank.

In some embodiments, recycling the portion of the ballasted solids fromthe solids-liquid separator to the reactor tank comprises recycling theportion of the ballasted solids from the solids-liquid separator to thereactor tank in an amount sufficient to generate an amount of metalhydroxide floc in the reactor tank sufficient to reduce a concentrationof dissolved metal in the reactor tank to below about 10micrograms/liter or to below about 5 micrograms/liter.

In some embodiments, the method further comprises introducing aflocculant into the reactor tank with the partially treated wastewater,ballast, and coagulent. The method may further comprise introducing anadsorbant into the reactor tank with the partially treated wastewater,ballast, flocculant, and coagulent.

In some embodiments, the method further comprises introducing anadsorbant into the reactor tank with the partially treated wastewater,ballast, and coagulent.

In some embodiments, the method further comprises introducing a metalprecipitant into the reactor tank with the partially treated wastewater,ballast, and coagulent.

In some embodiments, the method further comprises adjusting a pH of thepartially treated wastewater in the reactor tank to a pH at which acompound of the dissolved metal is substantially insoluble.

In accordance with another aspect, there is provided a method ofretrofitting a wastewater treatment system to facilitate increasedremoval of dissolved metals from wastewater. The method comprisesfluidly connecting a tertiary treatment sub-system to an outlet of asecondary treatment sub-system of the wastewater treatment system. Thetertiary treatment sub-system includes a reactor tank configured andarranged to receive the partially treated wastewater from the secondarytreatment sub-system, the reactor tank including at least one inlet andan outlet, a source of a ballast material fluidly connected to thereactor tank, a source of coagulant fluidly connected to the reactortank, a solids-liquid separator having an inlet fluidly connected to theoutlet of the reactor tank and including a solids-lean effluent outletand a ballasted solids outlet, the solids-liquid separator configured toseparate ballasted effluent from the outlet of the reactor tank into asolids-lean effluent and ballasted solids, to discharge the solids-leaneffluent from the solids-lean effluent outlet, and to discharge theballasted solids from the ballasted solids outlet, a recycle conduithaving an inlet fluidly connected to the ballasted solids outlet, and anoutlet fluidly connected to the reactor tank, and a controllerconfigured to recycle a portion of the ballasted solids from theballasted solids outlet of the solids-liquid separator to the reactortank through the recycle conduit in an amount sufficient to generate anamount of metal hydroxide floc in the reactor tank sufficient to reducea concentration of dissolved metal in the reactor tank.

In some embodiments, the method further comprises providing instructionsto configure the controller to recycle a portion of the ballasted solidsfrom the ballasted solids outlet of the solids-liquid separator to thereactor tank through the recycle conduit in an amount sufficient togenerate an amount of metal hydroxide floc in the reactor tanksufficient to reduce a concentration of dissolved metal in the reactortank to below about 5 micrograms/liter.

In some embodiments, the method further comprises fluidly connecting asource of metal precipitant to the reactor tank and/or fluidlyconnecting a source of pH adjustment agent to the reactor tank.

In some embodiments, the method further comprises providing instructionsto program the controller to control a quantity of pH adjustment agentintroduced into the reactor tank to achieve a pH in the reactor tank atwhich a compound including an undesirable metal in the partially treatedwastewater is substantially insoluble.

In some embodiments, the method further comprises fluidly connecting asource of flocculant to the reactor tank and/or fluidly connecting asource of adsorbant to the reactor tank.

DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. Forpurposes of clarity, not every component may be labeled in the drawings,nor is every component of each embodiment of the disclosure shown whereillustration is not necessary to allow those of ordinary skill in theart to understand the disclosure.

In the drawings:

FIG. 1 presents a schematic of a wastewater treatment system; and

FIG. 2 presents a schematic of an alternative secondary treatmentsub-system of the wastewater treatment system of FIG. 1.

DETAILED DESCRIPTION

This disclosure is directed to systems and methods of treating water orwastewater to, for example, reduce the concentration of metals in thewater or wastewater, and render the water suitable for secondary uses ordischarge to the environment. One or more aspects relate to wastewatertreatment systems and methods of operation and facilitating operation ofsame. The disclosure is not limited to the details of construction andthe arrangement of components, systems, or sub-systems set forth hereinand is capable of being practiced or of being carried out in variousways.

One or more aspects relate to wastewater treatment systems for treatingwastewater having an undesirably high contaminant level. For example,the wastewater treatment systems may be used for treating wastewaterhaving a high concentration of one or more heavy metals. Elevated heavymetal levels, as the term is used herein, may refer to dissolved heavymetal concentrations that may be higher than about 10 μg/l, or greater.Much of the heavy metals in wastewater may go untreated in conventionalwastewater treatment systems and may be discharged, resulting inpotential contamination of rivers, bays, and estuaries, and otherwaterways or water sources. Heavy metals are generally toxic to lifeforms, particularly aquatic life. Discharged untreated wastewater mayexceed discharge limits for various contaminants, for example,particular heavy metals, such as zinc or copper. The removal of heavymetals from wastewater has become very important with new stringentregulations that demand that levels in some jurisdictions be as low as 5μg/1 or less. Typical methods to remove metals have used precipitationby way of a metal hydroxide floc often with the use of precipitatingagents, for example, sodium sulfide and pH adjustment agents. Theseprecipitating agents and pH adjustment agents may themselves beundesirable contaminants and may be expensive to use. Accordingly, adesire exists to operate a wastewater treatment plant to removedissolved metals without the use of a significant amount of chemicalagents.

Contaminants that may be discharged with untreated wastewater mayinclude at least one of total suspended solids (TSS), biologicallyactive organic matter, microorganisms, for example, pathogens ornon-pathogens, nitrogen, phosphorous, and/or heavy metals. Heavy metalsare generally defined as metals with relatively high densities, atomicweights, or atomic numbers. Heavy metals tend to be less reactive thanlighter metals and have much less soluble sulfides and hydroxides. Heavymetals can be toxic in large amounts or in certain forms. In efforts toreduce the effects of heavy metals, many secondary use and point sourcedischargers have received more stringent effluent limits for heavymetals. Conventional processes precipitate heavy metals from thewastewater. The heavy metals may be precipitated as a hydroxide or as asulfide. Precipitation of heavy metals cannot reduce the heavy metalconcentration to at or below the lowest acceptable discharge levels.Heavy metal removal systems may remove heavy metals from wastewaterthrough the use of ballast materials.

One or more aspects of the present disclosure involve embodimentsdirected to the removal of or for the reduction of the level of one ormore contaminants from wastewater. One or more aspects of the disclosurerelate to wastewater treatment systems and methods of operation andmethods of modification thereof.

Typically, water to be treated, such as wastewater or a wastewaterstream, contains waste matter that, in some instances, can comprisesolids, soluble and insoluble organic and inorganic material, and heavymetals. Prior to discharge to the environment, such streams may betreated to decontaminate or at least partially render the wastewaterstreams benign or at least satisfactory for discharge under establishedregulatory requirements or guidelines. For example, the water can betreated to reduce its heavy metal content to within acceptable limits.

Systems and methods are provided for treating water or wastewater. Inaccordance with one or more embodiments, the disclosure relates to oneor more systems and methods for treating wastewater, wherein the heavymetal content of the wastewater to be treated exceeds a target value. Inaccordance with one or more embodiments, a recycle system is provided torecycle ballasted solids from treated effluent from a ballast reactortank to the wastewater treatment system. For example, a recycle systemmay be provided to recycle ballasted solids from the treated effluent tothe ballast reactor tank, source of ballast for the ballast reactortank, or a system upstream of the ballast reactor tank. The ballastedsolids may be separated from a solids-lean portion of the treatedeffluent prior to recycle in a solids-liquid separation system, forexample, a clarifier.

In accordance with one or more embodiments, the disclosure relates toone or more systems and methods for treating wastewater. The system mayreceive wastewater from a municipal or industrial source. For example,the wastewater may be delivered from a municipal or other large-scalesewage system.

In accordance with one or more embodiments, the disclosure relates toone or more systems and methods for retrofitting a wastewater treatmentsystem. Methods are provided for facilitating the treatment ofwastewater in a wastewater treatment system. In an embodiment, a methodcomprises providing a recycle line between the treated effluent from aballast reactor tank and the ballast reactor tank or source of ballastmaterial.

In some embodiments, a method of facilitating the treatment ofwastewater is provided. The wastewater treatment system may comprise aconduit connected to an outlet of a clarifier. The method may compriseproviding a recycle line fluidly connectable to treated effluentdownstream of the ballast system of the wastewater treatment system, therecycle line being configured to direct a portion of the ballastedsolids from the treated effluent to the ballast system. The ballastsystem may comprise a solids-liquid separator, for example, a clarifierconfigured to separate ballasted solids from effluent from the ballastsystem, and a recycle conduit to direct the separated ballasted solidsto a source of ballast material fluidly connected to an inlet of theballast reactor tank.

In some embodiments, operation of the wastewater treatment system maycomprise introducing wastewater from a source of wastewater to abiological reactor. As used herein, the term “biological reactor” is areactor having a population of microorganisms, which may include diversetypes of bacteria, used to decompose biodegradable material. Theconversion of pollutants or contaminants to innocuous compounds istypically facilitated or mediated by the microorganisms as thewastewater is passed through the wastewater treatment system. A biomassof microorganisms typically requires an environment that provides theproper conditions for growth or biological activity. A biologicalreactor may comprise a plurality of compartments or regions that may bepartitioned or not. For example, a biological reactor may compriseaerobic, anaerobic, and/or anoxic compartments or regions. Compartmentsof a biological reactor may comprise nitrification or denitrificationcompartments or regions. The size of the biological reactor may dependon the size of the wastewater treatment plant. For example, the size ofthe biological reactor may range from about 0.5 million gallons to about100 million gallons. The biological reactor may comprise one or morereactor vessels or tanks that are positioned in series or in parallel.Partially treated wastewater exiting the biological treatment system maycontain particulate or dissolved metals above a desired level fordischarge, for example, from about 10 μg/l to about 100 μg/l, dependingon the source of the wastewater and type of biological treatment used.

A ballasted wastewater treatment system may comprise a ballast reactortank configured to provide a ballasted effluent and a source of ballastmaterial fluidly connected to the ballast reactor tank. In someembodiments, the ballast system may comprise a source of coagulantfluidly connected to the ballast reactor tank. In some embodiments, theballasted system may comprise a source of flocculant fluidly connectedto the ballast reactor tank. In some embodiments, the ballasted systemmay comprise a source of adsorbant fluidly connected to the ballastreactor tank. The ballasted system may comprise a source of a chemical(referred to herein as a metal precipitant) fluidly connected to theballast reactor tank that facilitates precipitation of dissolved metalsor compounds thereof, for example, metal hydroxides, from liquid in theballast reactor tank. The addition of ballast, and optionally additionalcomponents such as flocculant, coagulant, adsorbant, and/or metalprecipitant improves the removal of dissolved, colloidal, particulate,and microbiological solids. The precipitation and enhanced settlabilityof ballasted solids provides for a more efficient, for example, smallerand/or faster, clarification step as compared to conventionalclarification systems, which may allow for a small footprint systemcomprising biological treatment, ballast treatment, and clarificationsteps.

Flocculation may be a process of contact and adhesion whereby particlesand colloids in liquid such as wastewater form larger-size clusters ofmaterial. Particles may cluster together in a floc. A flocculant maycomprise a material or a chemical that promotes flocculation by causingcolloids and particles or other suspended particles in liquids toaggregate, forming a floc. Polymers may be used as flocculants. Forexample, acrylic acid/acrylamide copolymers and modified polyacrylamidesmay be used.

Coagulation may be a process of consolidating particles, such ascolloidal solids. Coagulants may include cations. They may includecations such as aluminum, iron, calcium, or magnesium (positivelycharged molecules) that may interact with negatively charged particlesand molecules and reduce the barriers to aggregation. Examples ofcoagulants include bentonite clay, polyaluminum chloride, polyaluminumhydroxychloride, aluminum chloride, aluminum chlorohydrate, aluminumsulfate, ferric chloride, ferric sulfate, and ferrous sulfatemonohydrate.

Adsorption may be a physical and chemical process of accumulating asubstance at the interface between liquid and solids phases. Theadsorbant may be powdered activated carbon (PAC). PAC is an effectiveadsorbent because it is a highly porous material and provides a largesurface area to which contaminants may adsorb. PAC may have a diameterof less than about 0.1 mm and an apparent density ranging between about20 lb/ft′ and about 50 lb/ft³. PAC may have a minimum iodine number of500 as specified by AWWA standards.

According to some embodiments of the disclosure, a biological reactormay be used in conjunction with a ballasted treatment system to treatwater or wastewater. The systems and methods of the present disclosuremay be particularly advantageous, for example, in treatment plants wherea small footprint is desired such as, for example, a retrofit forindustrial plants, small flow plants or package plants, hybridwastewater plants, combining fixed film processes and activated sludgeprocesses, and lagoon plants requiring nitrification. The use of abiological reactor process in combination with ballasted settling is notlimited to the examples given. Many uses in biological and chemicaltreatment of wastewater or potable water are possible.

In certain embodiments, a biological reactor process followed by aballasted flocculation process may be utilized for biological treatmentof water or wastewater to remove at least one of nitrogen compounds,such as nitrates, biologically active organic matter, chemically activeorganic matter, phosphorous compounds, and/or heavy metals. Biologicalsolids produced may then be removed in addition to dissolved, colloidal,and particulate solids by clarifiers. In certain embodiments, heavymetals may be removed from the wastewater undergoing treatment toprovide treated wastewater prior to discharge to the environment orprior to disinfection to provide potable water or drinking water todistribute to a water supply grid.

Ballasted flocculation systems may comprise the addition of a ballast,and optionally, a coagulant and/or flocculant to improve the removal ofdissolved, colloidal, particulate, and microbiological solids. Incertain embodiments, the ballast may be a magnetic ballast.

In some embodiments, recirculation of ballasted solids to at least oneof the biological treatment process, ballasted flocculation processes,or to the source of ballast can further enhance the reliability of theoverall system. These features may be utilized in existing wastewatertreatment plants, small flow plants or package plants, combined seweroverflow (CSO) treatment plants, new plants that require a smallfootprint, and hybrid treatment plants (fixed film and activatedsludge). One benefit is that an existing clarifier downstream of abiological reactor process may be readily convertible to a ballastedsystem having ballasted solids recycle using the system of the presentdisclosure.

In some embodiments of the disclosure, a system for treating wastewateris provided. The system comprises a biological reactor fluidly connectedto a source of wastewater and configured to provide a biological reactoreffluent. The biological reactor effluent may flow to a ballastedflocculation system in which a source of coagulant may be fluidlyconnected to the biological effluent and configured to provide acoagulated effluent. A source of ballast may be fluidly connected to thecoagulated effluent and configured to provide a ballasted effluent. Insome embodiments, the source of ballast may be fluidly connected to atleast one of the biological effluent or the coagulated effluent.

The source of ballast may comprise a powdered ballast. The ballast maybe added to a ballasted reactor tank in dry powdered form. In someembodiments, the ballast may be added by an operator or by machinery,such as by a dry feeder. A clarifier may be fluidly connected to theballasted effluent outlet of a ballasted reactor tank. The clarifier maycomprise a treated effluent outlet and a ballasted solids outlet and maybe configured to separate ballasted effluent from the ballasted reactortank into a substantially ballast-free treated effluent and ballastedsolids. The ballasted solids outlet of the clarifier may be fluidlyconnected to the biological reactor, ballast reactor tank, or a sourceof ballast for the ballast reactor tank.

A source of flocculant may be fluidly connected to the ballast reactortank. At least one of the sources of coagulant, ballast, flocculant, andadsorbant may be provided in line to a biological reactor effluentstream. Alternately, tanks may be used such that the biological reactoreffluent flows to a coagulant tank, into which a coagulant is added froma source of coagulant. The coagulated effluent may then flow to aballast reactor tank, into which ballast is added from a source ofballast. The ballasted effluent may then flow to a flocculant tank, intowhich a flocculant is added from a source of flocculant. The flocculanteffluent may then flow to the clarifier. In certain embodiments, aflocculant tank and source of flocculant may not be included in theballasted flocculation system, and the ballasted effluent may flowdirectly to the clarifier. In some embodiments, a coagulant tank andsource of coagulant may not be included in the ballasted flocculationsystem.

As discussed above, the ballast may be a magnetic ballast. The magneticballast may comprise an inert material. The magnetic ballast maycomprise a ferromagnetic material. The magnetic ballast may compriseiron-containing material. In certain embodiments, the magnetic ballastmay comprise an iron oxide material. For example, the magnetic ballastmay comprise magnetite (Fe₃O₄). The magnetic ballast may have a particlesize that allows it to bind with biological and chemical flocs toprovide enhanced settling or clarification, and allow it to be attractedto a magnet so that it may be separated from the biological flocs. Theparticle size, e.g., the average diameter of the ballast, for example,the magnetic ballast, may be less than about 100 μm. In someembodiments, the particle size of the ballast, for example, the magneticballast, may be less than about 40 μm. In an embodiment, the particlesize of the ballast, for example, the magnetic ballast may be less thanabout 20 μm. The particle size of the ballast may be between about 80 toabout 100 μm, about 60 μm to about 80 μm, about 40 μm to about 60 μm,about 20 μm to about 40 μm, or about 1 μm to about 20 μm.

Sand ballasted systems often implement larger ballast sizes toeffectively recover the ballast. Sand ballast is non-magnetic. Sandballasted systems have implemented the use of cleaning agents toseparate the biological solids from the sand particles. This could be aresult of a large surface for bacteria to attach, requiring more thanshearing forces of a vortex mechanism alone to remove biological solidsfrom the sand particle surface, or the need to dissolve chemical bondsthat assist in the binding of the ballast.

Unlike sand-based ballast that requires growth of floc around relativelylarge size sand particles, magnetite ballast can be used with smallsize, such as less than about 100 μm, allowing for the magnetiteparticles to impregnate existing floc. The ballasted effluent or theflocculant effluent may be directed to at least one clarifier whereballasted solids, such as magnetite ballasted solids, may be removed bygravity at an enhanced rate greater than that of conventional gravityclarifiers. The clarifier, being configured to provide a treatedeffluent and a ballasted solids portion, may be fluidly connected to atleast one of the source of ballast, the ballasted reactor tank, thecoagulated effluent, and the biological reactor. This may allow at leasta portion of the ballasted solids to return to the ballast reactor tankand/or to the source of ballast, for example, a ballast tank connectedto a source of ballast. All or a portion of the biological solids mayalso be removed from the system. This may involve utilizing a ballastedrecovery system or wasting the biological solids prior to a ballastedrecovery system. In some embodiments, the ballasted recycle system maycomprise a magnetic separation apparatus, which may allow recycle ofmagnetic particles, which would not be feasible with, for example, sandparticles. In certain embodiments, mechanical shearing may be employedto shear the biological solids prior to ballast recycle, for example,prior to magnetite recycle. In some instances, such as re-seeding andhigh flow events, a portion of solids settled in a clarifier may berecycled to the front of the ballast reactor tank. These solids mayeither be ballasted or solids stripped of magnetite through the magneticseparation.

In certain embodiments, a ballast recycle system may be positioneddownstream of the ballasted solids outlet of the clarifier. The ballastrecycle system may be connected to the ballasted solids outlet of theclarifier and at least one of the source of ballast and the ballastreactor tank.

In certain embodiments, the use of a magnetic ballast providesadvantages over use of other ballast materials. For example, a magneticdrum may be used to separate the biological solids from the magneticballast in an efficient manner Optionally, mechanical shearing may beutilized prior to separation. This process may sufficiently remove thebiological solids from the ballast. Recycle of settled solids to theballast reactor tank further enhances performance and reliability, andallows for additional flexibility for treatability and recovery inprocess upsets or startups. In certain embodiments, cleaning solutionsare unnecessary in separating ballast from the heavy metals.

The present disclosure further comprises a recycle line. The recycleline may be connected to the ballasted solids outlet of the clarifierand at least one of the source of ballast and the ballast reactor tank.The recycle line may be configured to recycle the ballasted solids fromthe ballast effluent to at least one of the source of ballast and theballast reactor tank.

In some embodiments, process control systems may be used. Typically, thecontrol systems may be electrically connected to and may instruct valvesalong the recycle line to open and close. The control system may providefor adjustment of valves to adjust flow rates through one or more of thevalves. The control system may instruct valves along the recycle line toopen and close based on the use of a sensor configured to measure aproperty. The property may be a property of the system. For example, theproperty may be a concentration of one or more contaminants. Thecontaminant may be, for example, a heavy metal. The control system maystrategically adjust the degree of opening of one or more valves in therecycle line. For example, a valve in the recycle line may be at leastpartially opened to allow for a portion of ballasted solids to beintroduced to the source of ballast. In addition, a valve in the recycleline may be at least partially opened to allow for a portion of theballasted solids to be introduced to the ballast reactor tank. Thedegree of opening of the valves in the recycle line can influence theportions of ballasted effluent or ballasted solids introduced to thesource of ballast or the ballast reactor tank. Strategic management ofthe degree of opening of the valves may lead to overall improved removalof contaminants from the wastewater.

The control system may comprise one or more sensors. Non-limitingexamples of sensors suitable for use in the methods and systemsdescribed herein may include any sensor capable of detecting a propertyof the wastewater at any point within the treatment system. The sensormay be positioned, for example, so as to determine the heavy metalconcentration of the ballasted effluent. In certain embodiments, thesensors may detect or measure a process parameter and report the valueto the control system. The control system may be configured to comparethe detected or measured value with a target value. Responsive to aresult of the comparison, the control system may be configured to selecta degree of opening of valves in one or more conduits in the system.

In certain embodiments, the system may further comprise a measurementsystem. The measurement system may be in communication with the controlsystem. In some embodiments, the measurement system may function as oneor more components of a control system. The measurement system may be incommunication with one or more sensors in the treatment system, aspreviously discussed. In various embodiments, the measurement system maybe configured to measure one or more process parameters. For example,the measurement system may be configured to measure a level of heavymetals in the ballasted effluent. The measurement system may compriseone or more sensors. A portion of the ballasted effluent may be recycledto a at least one of the source of ballast and the ballast reactor tankbased at least in part on the property measurement.

In certain embodiments, a wastewater treatment system may be in place,and being operated conventionally. The wastewater treatment system mayencounter periods in which the system cannot adequately treat awastewater stream, for example, when the heavy metal concentration ofthe wastewater is high. It may be beneficial to retrofit the wastewatertreatment system with one or more systems of the present disclosure. Forexample, a recycle line may be put in place on an existing system sothat the recycle line may recycle some of the ballasted effluent orballasted solids to at least one of the source of ballast and theballast reactor tank.

A system for treating wastewater is shown in FIG. 1, indicated generallyat 100. In accordance with any of the aforementioned aspects of thedisclosure, treatment system 100 may comprise one or more treatmentoperation units, which may include one or more biological reactionprocesses and one or more solids-reducing and solids-recycling systemsor processes. The wastewater treatment system 100 may include a primarytreatment portion or sub-system 100A, a secondary treatment portion orsub-system 100B, and a tertiary treatment portion or sub-system 100C.

The primary treatment sub-system 100A of the wastewater treatment system100 is fluidly connected or connectable to a source of wastewater 10 viaa conduit 12 and associated pumps and valves (not shown). The source ofwastewater 10 may be a municipal, industrial, or residential source. Thewastewater may be moved through the system by way of a pump upstream ordownstream of the system. The source of wastewater may contain wastematter that, in some instances, can comprise solids, one or moredissolved heavy metals, and soluble and insoluble organic and inorganicmaterial.

The primary treatment sub-system 100A includes a primary clarifier 15and/or a filter, for example, a sand bed filter, that removes largersolids, sand, and grit from wastewater from the source of wastewater 10.Waste solids separated from the wastewater in the primary treatmentsub-system 100A may be removed from the system via conduit 16 and sentfor disposal or further treatment.

After primary treatment, the wastewater is sent to the secondarytreatment sub-system 100B. The secondary treatment sub-system 100B mayinclude one or more biological treatment units 20. Biological treatmentunit 20 can be a reactor having an activated sludge to mix with theinfluent wastewater to form mixed liquor. The activated sludge can be abiological floc comprising a population of microorganisms capable ofdecomposing biodegradable material. For example, the activated sludgemay comprise bacteria. Depending on the desired effluent, biologicaltreatment unit or units 20 may be any one or more of aerated anoxic,aerobic, and anaerobic treatment units. In an embodiment, a biologicaltreatment unit 20 may include an aerated anoxic zone including anaerator 25 providing dissolved oxygen sufficient to maintain anoxicconditions and contributing to the movement of the contents of thebiological treatment unit 20 if desired. Optional aerator 25 is shown inFIG. 1, and may be connected to a source of gas. The source of gas maybe air, oxygen, or other gases typically used in biological treatmentprocesses.

The biological treatment unit(s) 20 may include a sensor S, or aplurality of such sensors, which are configured to measure a quality ofa mixed liquor contained in the biological treatment unit(s) 20. SensorS may measure, for example, the flow rate, volume, total suspendedsolids, total BOD, or species, for example, microorganism concentrationin the mixed liquor. Sensor S may measure the concentration of nitrateand/or ammonia in the mixed liquor. Sensor S is illustrated in FIG. 1 asbeing disposed within biological treatment unit(s) 20, however, in otherembodiments, any sensor S (or an additional sensor) can be provided onbiological treatment unit influent conduit 18 or on biological treatmentunit effluent conduit 22, for example. In some embodiments, it isdesirable to position sensor S at a location in biological treatmentunit(s) 20 where there is significant mixing of the contents ofbiological treatment unit(s) 20 to provide a representative measurementof the conditions within biological treatment unit(s) 20 as a whole.Sensor S may be placed at any position upstream or downstream of a unitoperation, or within a unit operation.

The one or more biological treatment units 20 may have a mixed liquoroutlet in fluid communication with a downstream solids-liquid separator,for example, clarifier 30, via conduit 22. The clarifier 30 may separatemixed liquor output from the one or more biological treatment units 20into a solids lean effluent and a solids rich activated sludge. Thesolids lean effluent may include less than about 30 mg/L of TSS and/orless than about 30 mg/L of BOD and may include concentrations of one ormore metals at levels above acceptable levels for discharge to theenvironment, for example, more than about 10 μg/L or more than about 5μg/L. In one embodiment, the TSS concentration may be less than 10 mg/L.In one embodiment, the BOD concentration may be less than 10 mg/L. Inone example, the total nitrogen concentration of the solids leaneffluent may be less than 3 mg/L. In another example, the totalphosphorous concentration of the solids lean effluent may be less than 1mg/L.

A portion of the activated sludge may be recycled from a sludge outletof the clarifier 30 back to one or more of the biological treatmentunits 20 via conduit 34 as return activated sludge. A second portion ofthe activated sludge output from the sludge outlet of the clarifier 30may be removed from the system via conduit 32 and sent for disposal orfurther treatment.

The solids lean effluent of the clarifier may be considered partiallytreated wastewater. The partially treated wastewater may be directed toa tertiary treatment sub-system 100C for further treatment, for example,for removal of residual metals from the partially treated wastewater.The partially treated wastewater may be directed through a conduit 36into a ballast reactor tank 35. In the ballast reactor tank 35, ballastfrom a source of ballast 65 may be added to the partially treatedwastewater to facilitate settling of residual contaminants from thepartially treated wastewater. In some embodiments, the ballast materialcan be a magnetic ballast. The magnetic ballast may comprise an inertmaterial. The magnetic ballast may comprise a ferromagnetic material.The magnetic ballast may comprise iron-containing material. In certainembodiments, the magnetic ballast may comprise an iron oxide material.For example, the magnetic ballast may comprise magnetite (Fe₃O₄). Themagnetic ballast may have a particle size that allows it to bind withchemical flocs to provide enhanced settling or clarification and allowit to be attracted to a magnet so that it may be separated from thechemical flocs. The particle size, for example, diameter of the magneticballast may be less than 100 μm. In some embodiments, the particle sizeof the magnetic ballast may be less than about 40 μm. In an embodiment,the particle size of the magnetic ballast may be less than about 20 μm.For example, the particle size may be between about 80 μm to about 100μm, about 60 μm to about 80 μm, about 40 μm to about 60 μm, about 20 μmto about 40 μm, or about 1 μm to about 20 μm. The particle size referredto herein may be an average particle size. In some embodiments, theballast material can consist of magnetite or consist essentially ofmagnetite. The ballast can be added in dry powdered form. In someembodiments, the ballast material may be added by an operator or bymachinery. For example, ballast material may be added by a dry feeder.

In some embodiments, ballast reactor tank 35 is fluidly connected to asource of flocculant 45. The flocculant may comprise a material or achemical that promotes flocculation by causing colloids and particles orother suspended particles in liquids to aggregate, forming a floc. Theflocculant may be a polymer. For example, the flocculant may be acrylicacid/acrylamide copolymers or modified polyacrylamides.

In some embodiments, ballast reactor tank 35 is fluidly connected to asource of coagulant 50. The coagulant may comprise cations that interactwith negatively charged particles and molecules that reduce the barriersto aggregation. For example, the coagulant may comprise aluminum, iron,calcium, or magnesium. The coagulant 16 may further comprise bentoniteclay, polyaluminum chloride, polyaluminum hydroxychloride, aluminumchloride, aluminum chlorohydrate, aluminum sulfate, ferric chloride,ferric sulfate, and ferrous sulfate monohydrate.

In some embodiments, ballast reactor tank 35 is fluidly connected to asource of adsorbant 55. The adsorbant may comprise an activated carbon.For example, the adsorbant may comprise powdered activated carbon.Adsorption may be described as a physical and chemical process ofaccumulating a substance at the interface between liquid and solidsphases. According to some embodiments, the adsorbent may be a powderedactivated carbon (PAC). PAC is an effective adsorbent because it is ahighly porous material and provides a large surface area to whichcontaminants may adsorb. PAC may have a diameter of less than 0.1 mm andan apparent density ranging between 20 and about 50 lbs/ft³. PAC mayhave a minimum iodine number of 500 as specified by AWWA (American WaterWorks Association) standards.

In some embodiments, ballast reactor tank 35 is fluidly connected to asource of a pH adjuster 60. The source of pH adjuster 60 may include oneor more of an acid, for example sulfuric acid, a base, for example,sodium hydroxide, or a buffering agent, for example, bicarbonate. Thesource of pH adjuster 60 may be used to adjust the pH of partiallytreated wastewater in the ballast reactor tank 35 to a pH at which oneor more undesirable contaminants or compounds thereof, for example, oneor more metal contaminants are substantially insoluble.

In some embodiments, ballast reactor tank 35 is fluidly connected to asource of a metal precipitant 70. The metal precipitant may be achemical that causes dissolved metals or compounds thereof toprecipitate from solution in the ballast reactor tank 35. The metalprecipitant may comprise or consist of, for example, sodium sulfate(Na₂S).

The ballast reactor tank 35 may include a sensor S, or a plurality ofsuch sensors, which are configured to measure a quality of partiallytreated wastewater contained in the ballast reactor tank 35. Sensor Smay measure, for example, the flow rate, volume, total suspended solids,pH, dissolved metal concentration, or concentration of flocculant,coagulant, or metal precipitant in the partially treated wastewatercontained in the ballast reactor tank 35. Sensor S is illustrated inFIG. 1 as being disposed within ballast reactor tank 35, however, inother embodiments, any sensor S (or an additional sensor) can beprovided on the ballast reactor tank 35 influent conduit 36 or oncontained in the ballast reactor tank 35 effluent conduit 38, forexample. In some embodiments, it is desirable to position sensor S at alocation in contained in the ballast reactor tank 35 where there issignificant mixing of the contents contained in the ballast reactor tank35 to provide a representative measurement of the conditions within theballast reactor tank 35 as a whole.

Ballasted effluent from the ballast reactor tank 35 can be directed fromballast reactor tank 35 to a solids-liquid separation unit, for example,clarifier 40. Clarifier 40 is configured to separate the ballastedeffluent into a treated wastewater portion and a ballasted solidsportion. The ballasted solids portion may include precipitated metalhydroxide. Treated wastewater from the clarifier 40 may be deliveredthrough outlet conduit 42 for discharge to the environment or for use aspotable water or drinking water after further disinfection if necessary.The treated wastewater may be delivered to, for example, surface watersor a processing plant. The treated wastewater may have a dissolved metalconcentration of less than about 10 μg/L of one or more heavy metals. Inone embodiment, the treated wastewater may include less than about 5μg/L of one or more heavy metals.

The ballasted solids portion of the ballasted effluent from the ballastreactor tank 35 may further be separated into a waste ballasted solidsportion that may be output from the system via waste solids conduit 46for disposal or further treatment, and a recycled ballasted solidsportion. The recycled ballasted solids portion may be returned to theballast reactor tank 35 via conduit 44 and/or to source of ballast 65via conduit 76. The recycled ballasted solids portion can further beseparated into discarded ballasted solids portion and a ballasted solidsrecovery portion by ballast material recovery system 75. The discardedballasted solids portion may be output from the system via waste solidsconduit 46 for disposal or further treatment. Ballast material recoverysystem 75 may comprise a magnetic separation apparatus. In certainembodiments, mechanical shearing may be employed through the use of amechanical shearer to shear chemical solids from the ballast in therecycled ballasted solids portion prior to ballast recovery, forexample, prior to magnetite recovery. For example, ballast materialrecovery system 75 may comprise a shear mill, a hydrocyclone and/or arotating drum comprising a fixed array of rare-earth magnets. An exampleof a magnetic drum that may be utilized in embodiments of the presentlydisclosed ballast recovery system is disclosed in co-owned PCTapplication Publication No. WO 2014/088620, titled “MAGNETIC DRUM INLETSLIDE AND SCRAPER BLADE” which is incorporated herein by reference inits entirety for all purposes. Ballast material recovery system 75 mayseparate a recovered ballast material portion from a waste solidsportion. The recovered ballast material portion can be returned to theballast reactor tank 35 via conduit 48 and/or to source of ballast 65via conduit 76.

Sensors S in the biological treatment unit(s) 20 and ballast reactortank 35 may communicate, electrically or otherwise, with a controller 80to provide the controller with signals corresponding to a property thecontents of the biological treatment unit(s) 20 and ballast reactor tank35. Controller 80 may control a quantity or rate of addition offlocculant, coagulant, adsorbant, pH adjuster, ballast, and/or metalprecipitant to the ballast reactor tank 35 from respective sources offlocculant, coagulant, adsorbant, pH adjuster, ballast, and metalprecipitant 45, 50, 55, 60, 65, and 70. The controller 80 may control aquantity or rate of addition of flocculant, coagulant, adsorbant, pHadjuster, ballast, and/or metal precipitant to the ballast reactor tank35 based on signals received from one or more sensors S in the system,for example, one or more sensors in the ballast reactor tank 35 orupstream or downstream of the ballast reactor tank 35. Controller 80 maycontrol the degree of opening of valves in the various conduits in thesystem. One or more of valves (not shown) may be connected to controller80, however, to avoid complication, the connections are not shown inFIG. 1.

The controller 80 of the systems disclosed herein may be implementedusing one or more computer systems. The computer system may be, forexample, a general-purpose computer such as those based on an Intel®CORE™ type processor or Intel® Atom™ type processor, a Motorola PowerPC®processor, a Sun UltraSPARC® processor, a Hewlett-Packard PA-RISC®processor, or any other type of processor or combinations thereof.Alternatively, the computer system may include specially-programmed,special-purpose hardware, for example, an application-specificintegrated circuit (ASIC) or controllers intended for analyticalsystems.

The computer system can include one or more processors typicallyconnected to one or more memory devices, which can comprise, forexample, any one or more of a disk drive memory, a flash memory device,a RAM memory device, or other device for storing data. The memory istypically used for storing programs and data during operation of thetreatment system and/or computer system. Software, including programmingcode that implements embodiments of the disclosure, can be stored on acomputer readable and/or writable nonvolatile recording medium, and thentypically copied into memory wherein it can then be executed by theprocessor. Components of the computer system may be coupled by aninterconnection mechanism, which may include one or more busses (e.g.,between components that are integrated within a same device) and/or anetwork (e.g., between components that reside on separate discretedevices). The interconnection mechanism enables communications (e.g.,data, instructions) to be exchanged between components of the computersystem. The computer system can also include one or more input devices,for example, sensors such as any of sensors S, a keyboard, mouse,trackball, microphone, touch screen, and one or more output devices, forexample, a printing device, display screen, or speaker. In addition, thecomputer system may contain one or more interfaces that can connect thecomputer system to a communication network (in addition or as analternative to the network that may be formed by one or more of thecomponents of the computer system).

According to one or more embodiments, the one or more input devices mayinclude sensors for measuring parameters. The sensors, valves, and/orpumps of the wastewater treatment system 100, or all of these componentsmay be connected to a communication network that is operatively coupledto the computer system.

Controller 80 can include one or more computer storage media such asreadable and/or writeable nonvolatile recording medium in which signalscan be stored that define a program to be executed by one or moreprocessors. Storage medium may, for example, be a disk or flash memory.Although the computer system may be one type of computer system uponwhich various aspects may be practiced, it should be appreciated thataspects and embodiments are not limited to being implemented insoftware, or on a general purpose computer system. Indeed, rather thanimplemented on, for example, a general purpose computer system, thecontroller, or components or subsections thereof, may alternatively beimplemented as a dedicated system or as a dedicated programmable logiccontroller (PLC) or in a distributed control system. Further, it shouldbe appreciated that one or more features or aspects may be implementedin software, hardware or firmware, or any combination thereof. Forexample, one or more segments of an algorithm executable by thecontroller can be performed in separate computers, which in turn, can becommunication through one or more networks.

In another embodiment of the secondary treatment sub-system, indicatedgenerally at 101B in FIG. 2, a ballast reactor tank 36 may be disposeddownstream of a solids-lean effluent outlet of clarifier 30. The ballastreactor tank 36 may receive ballast from a source of ballast 66 and/orrecycled ballast from a ballast recovery system 71 to facilitatesettling and removal of biological floc from the solids-lean effluentfrom clarifier 30. Sources of flocculant 46, coagulant 51, adsorbant 56,pH adjuster 61, and ballast 66 may be fluidly connected to ballastreactor tank 36 and may operate similarly to sources of flocculant 45,coagulant 50, adsorbant 55, pH adjuster 60, and ballast 65 fluidlyconnected to ballast reactor tank 35. A solids-liquid separator, forexample, clarifier 41 may separate ballasted effluent from the ballastreactor tank 36 into a ballasted solids portion from which ballast maybe recovered in ballast recovery system 71 and a solids lean partiallytreated wastewater to be sent for further processing in the tertiarytreatment sub-system 100C. Ballast recovery system 71 may besubstantially similar to the ballast recovery system 75 associated withthe ballast reactor tank 35.

EXAMPLES

A treatability study was conducted with the effluent from a tricklingfilter of a municipal wastewater treatment plant. The objective of thisstudy was to determine what additives could be used to achieve a totalcopper concentration of ≤14 ug/L in the treated supernatant. Four seriesof jar tests were conducted with the following added to the wastewatereffluent.

-   -   1. Baseline: Aluminum chlorohydrate (ACH)/ferric chloride        (ferric) coagulant with flocculent.    -   2. Baseline with pH Adjust: The targeted pH was 8, however, the        target was not fully achieved due to the instability of the        wastewater. In this series, there seems to be an outlier (Jar        9). This has been taken out when calculating averages.    -   3. Coagulant at 100 mg/L, pH Adjust, and Na₂S: Here again the pH        was targeted to 8, but did not hold up well.    -   4. Coagulant at 100 mg/L, pH Adjust, Na₂S, and recycled solids.        Simulated recycled solids were generated by adding ACH to        wastewater effluent in separate jars.

TABLE 1 Wastewater Quality (TF Effluent) Parameter (units) ConcentrationTSS (mg/L) 45.5  Total Phosphorous (mg/L)  6.63 Soluble Phosphorous(mg/L)  5.88 Total Cu (μg/L) 56.6  Soluble Cu (μg/L), 0.45 micron filter15.5  Tubidity (NTU) 34.1  pH (standard units)  7.19Series 1: This series was a baseline with a coagulant and a flocculent.Two coagulants (Ferric and ACH) were used. The flocculent used was ahigh molecular weight, high charge density, anionic.

TABLE 2 Baseline Concentration/Removal Percentage Parameter Jar 1 Jar 2Jar 3 Jar 3R Jar 4 Jar 5 Jar 6 ACH (mg/L) 25 65 100 100 Ferric (mg/L) 2565 100 pH 6.75 7.33 7.26 6.79 7.28 7.09 6.89 Flocculant (mg/L 1 1 1 1 11 1 Turbidity (NTU) 0.60 0.23 0.16 2.80 1.69 0.69 TSS (mg/L) 1.75 1.01.0 2.5 3.1 0.95 2.0 TSS % Removal 96% 98% 98% 95% 93% 98% 96% TotalPhosphorous 0.152 0.086 0.054 0.071 0.286 0.170 0.072 (mg/L) TotalPhosphorous 98% 99% 99% 99% 96% 97% 99% % Removal Soluble Phosphorous0.131 0.083 0.044 0.066 0.239 0.158 0.034 (mg/L) Soluble Phosphorous 98%99% 99% 99% 96% 97% 99% % Removal Total Cu (μg/L) 13.7 14.8 12.5 15.116.2 Total Cu % Removal 76% 74% 78% 73% 71% Soluble Cu (μg/L) 14.4 11.111.2 8.2 13.7 Soluble Cu %  7% 28% 28% 47% 12% Removal

Observation:

Total Cu removal with Ach addition averages 75% with very littlevariation with changing ACH dose. Soluble Cu removal averages 28%,however, it increases with the ACH dose. The greater concentration ofhydroxide floc generated by the higher ACH dose may allow for greateradsorption of the soluble copper content.

Series 2: In this series the pH was adjusted to a target of 8 to mimicthe minimum solubility conditions for Cu. However, the aforementioned pHcondition was not fully met.

TABLE 3 Baseline with pH Adjust Concentration/Removal PercentageParameter Jar 7 Jar 8 Jar 9 Jar 9R Jar 10 Jar 11 Jar 12 ACH (mg/L) 25 65100 100 Ferric (mg/L) 25 65 100 pH 7.25 7.5 7.37 7.72 7.28 7.05 6.92Flocculant (mg/L 1 1 1 1 1 1 1 Turbidity (NTU) 0.79 0.39 0.19 3.12 1.750.49 TSS (mg/L) 3.0 1.3 0.75 1.0 4.2 3.0 1.5 TSS % Removal 93% 97% 98%98% 91% 93% 97% Total Phosphorous 0.375 0.168 0.088 0.166 0.48 0.2130.08 (mg/L) Total Phosphorous 94% 97% 99% 97% 93% 97% 99% % RemovalSoluble Phosphorous 0.332 0.156 0.080 0.163 0.388 0.177 0.047 (mg/L)Soluble Phosphorous 94% 97% 99% 97% 93% 97% 99% % Removal Total Cu(μg/L) 13.4 13.9 10.9 10.8 19.2 Total Cu % Removal 76% 75% 81% 81% 66%Soluble Cu (μg/L) 13.6 11.4 11.6 10.2 13.2 Soluble Cu % 12% 26% 25% 34%15% Removal

Observation:

Total Cu removal with ACH addition averages 78%. Similar to series 1,very little variation with changing ACH dose. The total Cu removalpercentage is slightly higher than in series 1 (no pH adjust). However,it should be noted that the targeted pH condition was not fullyachieved.

The soluble Cu removal percentage averages 25%, lower than the 28%achieved in series 1. Similar to series 1, it follows the dose responsenoted.

JAR 9R does get to a pH of 7.72 with an 81% total Cu and 34% soluble Curemoval, respectively. JAR 9 performs similarly with total Cu with a pHof 7.37.

Series 3: In this series a coagulant dose of 100 mg/L was used with thepH adjusted to a target of 8. Here again, the aforementioned pHcondition was not fully met due to unstable conditions. Na₂S chemistrywas introduced in this series as a mechanism for Cu removal.

TABLE 4 Baseline, pH Adjust with Na₂S Chemistry Concentration/RemovalPercentage Parameter Jar 13 Jar 14 Jar 15 Jar 16 Jar 17 Jar 18 ACH(mg/L) 100 100 100 Ferric (mg/L) 100 100 100 pH 7.50 7.54 7.56 7.05 6.907.00 Na₂S (mg/L) 10 25 50 10 25 50 Flocculant 1 1 1 1 1 1 (mg/LTurbidity (NTU) 0.29 0.19 0.18 1.25 4.85 13.05 TSS (mg/L) 0.95 0.88 1.043.71 4.0 3.75 TSS % Removal 98% 98% 98% 92% 91% 92% Total 0.226 0.1900.174 0.14 0.136 0.13 Phosphorous (mg/L) Total 97% 97% 97% 98% 98% 98%Phosphorous % Removal Soluble 0.221 0.189 0.168 0.069 0.110 0.070Phosphorous (mg/L) Soluble 96% 97% 97% 99% 98% 99% Phosphorous % RemovalTotal Cu (μg/L) 15.4 12.8 14.8 18.1 Total Cu % 73% 77% 74% 68% RemovalSoluble Cu 9.6 10.4 8.1 9.8 (μg/L) Soluble Cu % 38% 33% 48% 37% Removal

Observation:

Total Cu removal with ACH addition averages 75%. There is very littlevariation in total Cu removal with varying Na₂S dose.

The soluble Cu removal percentage averages 40%, higher than thatachieved in series 1 and 2.

Series 4: In this series additional amounts of solids were used to mimicthe recycle of hydroxide floc to a solids removal reactor. Simulatedrecycled solids were generated by adding ACH to wastewater effluent inseparate jars. In this series an ACH dose of 100 mg/L was used. pH wasadjusted to approach 8 in JAR 22 and 23 only. Na₂S was introduced.

TABLE 5 Baseline, pH Adjust with Na2S Chemistry and High SolidsConcentration/Removal Percentage Parameter Jar 21 Jar 22 Jar 23 ACH(mg/L) 100 100 100 pH 7.12* 7.93 8.65 Na₂S (mg/L) 25 25 50 Flocculant(mg/L 1 1 1 TSS (mg/L) 4.00 0.67 2.25 TSS % Removal 91% 99% 95% TotalPhosphorous (mg/L) 0.064 0.104 0.384 Total Phosphorous % Removal 99% 98%94% Soluble Phosphorous (mg/L) 0.026 0.101 0.368 Soluble Phosphorous %Removal 100% 98% 94% Total Cu (μg/L) 9.0 9.5 9.2 Total Cu % Removal 84%83% 84% Soluble Cu (μg/L) <5 7.4 5.2 Soluble Cu % Removal >68% 52% 66%*pH was not adjusted

Observation:

Total Cu removal with ACH addition averages 84%, higher compared toprevious series. The soluble Cu removal percentage averages >62%, muchhigher than previous series.

CONCLUSIONS

Data is averaged for each series below.

TABLE 6 Results Summary Total Cu % Soluble Cu % Series ConcentrationRemoval Concentration Removal Baseline 14.0  75% 11.2  28% Baseline +12.3  78% 11.7  25% pH Adjust Baseline + pH 14.3  75% 9.4 40% Adjust +Na₂S Baseline + pH 9.2 84% <5.9  >62%  Adjust + Na₂S + Solids Recycle

Recycled solids content is driving the total and soluble Cu removalefficiencies more than Na₂S chemistry or pH adjustment. This phenomenonis clear in both total and soluble Cu removal. All three jars to whichrecycled solids were added exhibited <10 μg/L for total Cu and <8 μg/Lfor soluble Cu (series 4).

The average soluble Cu concentration for all ACH addition tests when norecycled solids are introduced is 10.9 μg/L (30% removal) vs. <5.9 μg/L(>62% removal) when recycled solids are introduced.

The average total Cu concentration for all ACH addition tests when norecycled solids are introduced is 13.5 μg/L (76% removal) vs. 9.2 μg/L(84% removal) when recycled solids are introduced. Total Cu removalpercentage improvement with addition of recycled solids was not aspronounced as soluble Cu removal percentage.

The methods and systems described herein are not limited in theirapplication to the details of construction and the arrangement ofcomponents set forth in the previous description or illustrations in thefigures. The methods and systems described herein are capable of otherembodiments and of being practices or of being carried out in variousways. Also, the phraseology and terminology used herein is for thepurpose of description and should not be regarded as limiting. The useof “including,” “comprising,” “having,” “containing,” “involving,”“characterized by,” “characterized in that,” and variations thereofherein is meant to encompass the items listed thereafter, equivalentsthereof, as well as alternate embodiments consisting of the items listedthereafter exclusively.

Use of ordinal terms such as “first,” “second,” “third,” and the like inthe specification and claims to modify an element does not by itselfconnote any priority, precedence, or order of one element over anotheror the temporal order in which acts of a method are performed, but areused merely as labels to distinguish one element having a certain namefrom another element having a same name, but for use of the ordinalterm, to distinguish the elements.

Those skilled in the art would readily appreciate that the variousparameters and configurations described herein are meant to be exemplaryand that actual parameters and configurations will depend upon thespecific application for which the apparatus and methods of the presentdisclosure are used. Those skilled in the art will recognize, or be ableto ascertain using no more than routine experimentation, manyequivalents to the specific embodiments described herein. For example,those skilled in the art may recognize that the system, and componentsthereof, according to the present disclosure may further comprise anetwork of systems or be a component of a water treatment system. It is,therefore, to be understood that the foregoing embodiments are presentedby way of example only and that, within the scope of the appended claimsand equivalents thereto, the disclosed systems and methods may bepracticed otherwise than as specifically described. The present systemsand methods are directed to each individual feature, system, or methoddescribed herein. In addition, any combination of two or more suchfeatures, systems, or methods, if such features, systems, or methods arenot mutually inconsistent, is included within the scope of the presentdisclosure. The steps of the methods disclosed herein may be performedin the order disclosed or in alternate orders and the methods mayinclude additional or alternative acts or may be performed with one ormore of the disclosed acts omitted.

Further, it is to be appreciated that various alterations,modifications, and improvements will readily occur to those skilled inthe art. Such alterations, modifications, and improvements are intendedto be part of this disclosure, and are intended to be within the spiritand scope of the disclosure. In other instances, an existing facilitymay be modified to utilize or incorporate any one or more aspects of themethods and systems described herein. Accordingly, the foregoingdescription and figures are by way of example only. Further, thedepictions in the figures do not limit the disclosures to theparticularly illustrated representations.

While exemplary embodiments of the disclosure have been disclosed, manymodifications, additions, and deletions may be made therein withoutdeparting from the spirit and scope of the disclosure and itsequivalents, as set forth in the following claims.

What is claimed is:
 1. A system for treating wastewater, the systemcomprising: a primary treatment sub-system; a secondary treatmentsub-system in fluid communication downstream of the primary treatmentsub-system, the secondary treatment sub-system configured to removebiological contaminants from the wastewater and produce a partiallytreated wastewater including a dissolved metal; and a tertiary treatmentsub-system in fluid communication downstream of the secondary treatmentsub-system, the tertiary treatment sub-system comprising: a reactor tankconfigured and arranged to receive the partially treated wastewater fromthe secondary treatment sub-system, the reactor tank including at leastone inlet and an outlet; a source of a ballast material fluidlyconnected to the reactor tank; a source of coagulant fluidly connectedto the reactor tank; a solids-liquid separator having an inlet fluidlyconnected to the outlet of the reactor tank and including a solids-leaneffluent outlet and a ballasted solids outlet, the solids-liquidseparator configured to separate ballasted effluent from the outlet ofthe reactor tank into a solids-lean effluent and ballasted solids, todischarge the solids-lean effluent from the solids-lean effluent outlet,and to discharge the ballasted solids from the ballasted solids outlet;a recycle conduit having an inlet fluidly connected to the ballastedsolids outlet, and an outlet fluidly connected to the reactor tank; anda controller configured to recycle a portion of the ballasted solidsfrom the ballasted solids outlet of the solids-liquid separator to thereactor tank through the recycle conduit in an amount sufficient togenerate an amount of metal hydroxide floc in the reactor tanksufficient to reduce a concentration of dissolved metal in the reactortank.
 2. The system of claim 1, wherein the controller is configured torecycle the portion of the ballasted solids from the ballasted solidsoutlet of the solids-liquid separator to the reactor tank through therecycle conduit in an amount sufficient to generate an amount of metalhydroxide floc in the reactor tank sufficient to reduce a concentrationof dissolved metal in the reactor tank to below about 10micrograms/liter.
 3. The system of claim 2, wherein the controller isconfigured to recycle the portion of the ballasted solids from theballasted solids outlet of the solids-liquid separator to the reactortank through the recycle conduit in an amount sufficient to generate anamount of metal hydroxide floc in the reactor tank sufficient to reducea concentration of dissolved metal in the reactor tank to below about 5micrograms/liter.
 4. The system of claim 2, wherein the controller isconfigured to recycle between about 5% and about 25% of ballasted solidsseparated from the ballasted effluent in the solids-liquid separator tothe reactor tank.
 5. The system of claim 4, wherein the controller isconfigured to recycle about 10% of ballasted solids separated from theballasted effluent in the solids-liquid separator to the reactor tank.6. The system of claim 1, further comprising a source of a metalprecipitant in fluid communication with the reactor tank.
 7. The systemof claim 6, wherein the metal precipitant is a sulfide-containingcompound.
 8. The system of claim 1, further comprising a source of a pHadjustment agent in fluid communication with the reactor tank.
 9. Thesystem of claim 8, wherein the controller is further configured tocontrol a quantity of pH adjustment agent introduced into the reactortank to achieve a pH in the reactor tank at which a compound includingthe dissolved metal is substantially insoluble.
 10. The system of claim1, further comprising a source of a flocculant in fluid communicationwith the reactor tank.
 11. The system of claim 10, further comprising asource of an adsorbant in fluid communication with the reactor tank. 12.The system of claim 11, further comprising a source of a pH adjustmentagent in fluid communication with the reactor tank.
 13. The system ofclaim 1, further comprising a source of an adsorbant in fluidcommunication with the reactor tank.
 14. The system of claim 1, furthercomprising a ballast recovery system in fluid communication with theballasted solids outlet of the solids-liquid separator, the ballastrecovery system configured to separate ballast from the ballasted solidsand return the separated ballast to one of the reactor tank and thesource of ballast material.
 15. The system of claim 1, wherein thesecondary treatment system comprises: a second reactor tank configuredand arranged to remove biological contaminants from the wastewater; anda ballast recycle system configured to return a portion of ballastedsolids output from the second reactor tank to the second reactor tank.16. A method for treating wastewater, the method comprising: treatingthe wastewater in primary treatment sub-system and a secondary treatmentsub-system to produce a partially treated wastewater having a reducedconcentration of organic contaminants as compared to the wastewater andincluding a dissolved metal; introducing the partially treatedwastewater into a reactor tank with a ballast material and a coagulantto form ballasted solids; introducing a ballasted effluent from thereactor tank including the ballasted solids into a solids-liquidseparator; separating the ballasted effluent into ballasted solids and asolids-lean effluent in the solids-liquid separator; and recycling aportion of the ballasted solids from the solids-liquid separator to thereactor tank in an amount sufficient to generate an amount of metalhydroxide floc in the reactor tank sufficient to reduce a concentrationof dissolved metal in the reactor tank.
 17. The method of claim 16,wherein recycling the portion of the ballasted solids from thesolids-liquid separator to the reactor tank comprises recycling theportion of the ballasted solids from the solids-liquid separator to thereactor tank in an amount sufficient to generate an amount of metalhydroxide floc in the reactor tank sufficient to reduce a concentrationof dissolved metal in the reactor tank to below about 10micrograms/liter.
 18. The method of claim 17, wherein recycling theportion of the ballasted solids from the solids-liquid separator to thereactor tank comprises recycling the portion of the ballasted solidsfrom the solids-liquid separator to the reactor tank in an amountsufficient to generate an amount of metal hydroxide floc in the reactortank sufficient to reduce a concentration of dissolved metal in thereactor tank to below about 5 micrograms/liter.
 19. The method of claim16, further comprising introducing a flocculant into the reactor tankwith the partially treated wastewater, ballast, and coagulent.
 20. Themethod of claim 19, further comprising introducing an adsorbant into thereactor tank with the partially treated wastewater, ballast, flocculant,and coagulent.
 21. The method of claim 16, further comprisingintroducing an adsorbant into the reactor tank with the partiallytreated wastewater, ballast, and coagulent.
 22. The method of claim 16,further comprising introducing a metal precipitant into the reactor tankwith the partially treated wastewater, ballast, and coagulent.
 23. Themethod of claim 16, further comprising adjusting a pH of the partiallytreated wastewater in the reactor tank to a pH at which a compound ofthe dissolved metal is substantially insoluble.
 24. A method ofretrofitting a wastewater treatment system to facilitate increasedremoval of dissolved metals from wastewater, the method comprising:fluidly connecting a tertiary treatment sub-system to an outlet of asecondary treatment sub-system of the wastewater treatment system, thetertiary treatment sub-system including: a reactor tank configured andarranged to receive the partially treated wastewater from the secondarytreatment sub-system, the reactor tank including at least one inlet andan outlet; a source of a ballast material fluidly connected to thereactor tank; a source of coagulant fluidly connected to the reactortank; a solids-liquid separator having an inlet fluidly connected to theoutlet of the reactor tank and including a solids-lean effluent outletand a ballasted solids outlet, the solids-liquid separator configured toseparate ballasted effluent from the outlet of the reactor tank into asolids-lean effluent and ballasted solids, to discharge the solids-leaneffluent from the solids-lean effluent outlet, and to discharge theballasted solids from the ballasted solids outlet; a recycle conduithaving an inlet fluidly connected to the ballasted solids outlet, and anoutlet fluidly connected to the reactor tank; and a controllerconfigured to recycle a portion of the ballasted solids from theballasted solids outlet of the solids-liquid separator to the reactortank through the recycle conduit in an amount sufficient to generate anamount of metal hydroxide floc in the reactor tank sufficient to reducea concentration of dissolved metal in the reactor tank.
 25. The methodof claim 24, further comprising providing instructions to configure thecontroller to recycle a portion of the ballasted solids from theballasted solids outlet of the solids-liquid separator to the reactortank through the recycle conduit in an amount sufficient to generate anamount of metal hydroxide floc in the reactor tank sufficient to reducea concentration of dissolved metal in the reactor tank to below about 5micrograms/liter.
 26. The method of claim 24, further comprising fluidlyconnecting a source of metal precipitant to the reactor tank.
 27. Themethod of claim 24, further comprising fluidly connecting a source of pHadjustment agent to the reactor tank.
 28. The method of claim 27,further comprising providing instructions to program the controller tocontrol a quantity of pH adjustment agent introduced into the reactortank to achieve a pH in the reactor tank at which a compound includingan undesirable metal in the partially treated wastewater issubstantially insoluble.
 29. The method of claim 24, further comprisingfluidly connecting a source of flocculant to the reactor tank.
 30. Themethod of claim 24, further comprising fluidly connecting a source ofadsorbant to the reactor tank.